VI. INGRESS AND EGRESS OF AIR.—Doors and windows, the only sources for the ingress of air in ordinary apartments, should be avoided as a means of introducing air in all new buildings, and independent apertures and flues provided, entirely under the control of valves, by whose action the amount of ingress can be regulated with precision. Further, in every apartment foul air should be led from the greatest altitude by similar independent flues. The ordinary construction often interferes seriously with ventilation, foul air descending sometimes in one and escaping in another. An alteration in the structure of houses, introducing one principal chimney, in which the flues from all the apartments ultimately join, would be a great improvement in this respect; and even for whole streets and districts one large shaft would be sufficient. To any who studies attentively the movement of currents of air, numerous other changes will present themselves as being equally desirable in the habitations of the rich and of the poor. In public buildings, the foul air, from hundreds of apartments, will be removed by a single shaft.
The reader who is anxious to extend his knowledge of this subject, will find much information in the Parliamentary Reports, particularly on the Ventilating and Acoustic arrangements of the present House of Commons, on the Ventilation of Mines, in many of the Reports on Education and on Manufactures, in which the health of the children has more particularly engaged attention; in the Reports on Improving the Health of Large Towns, and in some Statistical Reports on the Health of the Army and Navy. Tredgold on Warming and Ventilating, is a work of great value, and the different memoirs and treatises of D'Arcet, present numerous important details. In Dr Arnott's work on Warming and Ventilating, a full description of his stove is given; and in Hood's, and also Richardson's treatise on the same subjects, the different varieties of hot water apparatus are explained. In Dr Reid's Chemistry of the Atmosphere, and Illustrations of Warming and Ventilating, the result of numerous experiments is given on the ventilation of public buildings and private dwelling-houses, and the ventilation of ships, manufactories, &c.
The laws of the communication of heat, the electrical condition of the atmosphere, the diffusion of gases, the fluctuations of the barometer, the indications of the hygrometer; the plenum movement, when the pressure of the air within, from mechanical means, exceeds that without the apartment ventilated; the vacuum movement, when the reverse is induced; the downward and lateral current, especially the former, which is so important in protecting works of art exposed in public assemblies; the precautions necessary where it may be introduced, the influence of different
varieties of clothing, of medicated atmospheres, of moist and dry air baths at different temperatures, and of fumigation, are all objects of inquiry that bear practically on ventilation. The peculiar arrangements in various mines, hospitals, and manufactories, especially where offensive vapours are condensed or destroyed, likewise afford many valuable illustrations of its practice. (p. o.)